Conventionally, discussions have been made on small base station apparatuses to be installed in homes or offices. A small base station apparatus is used for connection with fixed lines for homes to widen the communication area or provide user-specific services. A small base station apparatus according to the standardization group 3GPP (3rd Generation Partnership Project) is called a home node B (or a home (e) node B). Among home nodes B, a home node B that limits users who can use the node by prior registration of access-permitted users, is particularly called a CSG (Closed Subscriber Group) cell (Non-Patent Document 1).
In 3GPP, a discussion is progressing on a CSG cell for ‘EUTRA (Evolved Universal Terrestrial Radio Access)’ having been evolved from the third generation mobile communication system and ‘Advanced EUTRA’ advanced therefrom. Unless a mobile station apparatus can distinguish among CSG cells for which subscribers are registered, CSG cells for which subscribers are not registered, and normal cells, the mobile station apparatus tries access to inaccessible CSG cells, resulting in a waste of power consumption and radio resources.
Further, because handover to a cell other than the registered CSG cells is not normally permitted for a mobile station apparatus, it is necessary for the mobile station apparatus to recognize a type of the cell in advance. As methods for a mobile station apparatus to distinguish CSG cells from normal cells, there are proposed methods, including a method that includes a CSG cell identifier in broadcast information (section 6.3.1 of Non-Patent Document 2), a method that performs distinguishing with a cell ID judged by a synchronization signal (Non-patent Document 3), and a method that allocates to a CSG cell a frequency different from that to a normal cell (Non-patent Document 4).
FIG. 17 is a diagram showing an example of a sequence chart that illustrates the measurement of a neighboring cell and a measurement report by a mobile station apparatus, when a CSG cell is disposed as a neighboring cell. The mobile station apparatus receives a synchronization signal-s (step S1701), a downlink reference signal-s (step S1702), and broadcast information channel-s (step S1703) from a base station apparatus (source cell), and then starts communication with the source cell (step S1704), wherein the mobile station apparatus and the source cell are in a state of communication with each other (active state).
Herein, the mobile station apparatus obtains CSG cell information from the neighboring CSG cell deployed in the mobile station apparatus (step S1705). CSG cell information is information obtained by the mobile station apparatus from a signal transmitted from a CSG cell by a method according to any one of Non-Patent Documents 2 to 4, to distinguish a normal cell from a CSG cell. For example, in Non-Patent Document 2, CSG cell information indicates a CSG cell identifier of broadcast information. Likewise, in Non-Patent Documents 3 and 4, CSG cell information respectively corresponds to a cell ID and a frequency band.
The mobile station apparatus, in neighboring cell measurement processing (step S1706), recognizes a CSG cell by a CSG cell identifier, eliminates unregistered CSG cells from target base station apparatuses of neighboring cell measurement, and transmits a measurement report, which is a radio signaling message, to the source cell without including the CSG cells in a measurement report message (step S1707). That is, the mobile station apparatus does not perform measurement processing of downlink reference signals of the unregistered CSG cells.
FIG. 18 is a diagram showing an example of a flowchart illustrating the operation of the mobile station apparatus in the measurement processing of neighboring cells. The mobile station apparatus receives neighboring cell signals from the neighboring cells (step S1801). From a result of reception and demodulation of the neighboring cell signals, it is determined by CSG cell identifiers whether unregistered CSG cells are included in the neighboring cells (step S1802), and when unregistered CSG cells are included, the measurement processing of the downlink reference signals of the CSG cells is stopped on the unregistered CSG cells (step S1803). On the other hand, when it is determined that no unregistered CSG cells are included in step S1802, then the measurement processing of measurement signals is executed on all the neighboring cells (step S1804).